The present invention relates to a method and apparatus for generating a supply of a liquid in vaporous state borne by carrier gas.
In making foundry sand cores by the cold box method, a foundry mix of sand and a binder is prepared and shaped. The shaped green core then is gased with a vaporous amine which is carried by air or an inert carrier gas under pressure. The vaporous amine curing agent cures the binder which can be phenolic or other polyol resin in admixture with a multi-isocyanate cross-linking agent. Vaporous tertiary amine catalysts also are required for curing surface coating compositions of a polyol and multi-isocyanate dispersed in a solvent therefor. Such vapor permeation curing technology traditionally has been practiced by containing the amine vapors within a curing chamber through which is passed a coated substrate. A new and alternative approach to the curing chamber involves the concurrent generation of an atomizate of the coating composition and a carrier gas bearing a catalytic amount of the vaporous tertiary amine. The thus-generated gas flow and atomizate are mixed and directed onto a substrate for curing. This modified spray procedure requires the generation of a carrier gas flow bearing the catalytic vaporous tertiary amine of precisely-controlled composition and pressure for use with conventional spray equipment. Such vaporous spray coating process is disclosed by Blegen in commonly-assigned application Ser. No. 06/474,156, filed Mar. 10, 1983 now abandoned.
Traditionally, a variety of methods have been proposed in the art for generating a supply of a carrier gas saturated with vapors of a liquid reactive or catalytic material. In the foundry core area, such techniques have included the pump liquid-injector method wherein liquid amine is injected into an air stream under pressure. Another typical apparatus is know as a bubbler and operates by passing an inert carrier gas through a liquid reservoir of the amine, such as shown in U.S. Pat. Nos. 3,590,902; 4,051,886; and 4,105,725. In other technical areas, vapor generators have been used to supply vapors of materials such as SiCl.sub.4, and GeCl.sub.4, and POCl.sub.3, for example. One such system is shown in U.S. Pat. No. 4,276,243. Of course, a discussion of vapor generators would not be complete without reference to humidification generation, such as shown in U.S. Pat. No. 3,962,381.
While a variety of successful vapor generators have been proposed, problems in reliably delivering a specified concentration of vaporous liquid in the carrier gas stream still is lacking in the art. Additionally, traditional vapor generators do not permit the generator vessel to be operated at one pressure while the resulting vaporous gas flow withdrawn therefrom is being delivered at a different pressure. This latter pressure restriction is important in the vaporous spray process noted above.